1. Field of the Invention
This invention relates to a belt tightener for seat belts in vehicles, comprising a device for moving the belt buckle in a belt-tightening sense and for locking the belt buckle at the end of the tightening movement, which device is activated by a so-called vehicle-sensitive system is response to an acceleration or deceleration in excess of predetermined critical values.
2. Description of the Prior Art
The safety which is afforded by seat belts in vehicles can be increased further by the provision of a belt tightener, which serves to tighten the seat belt in response to the acceleration or deceleration which occurs immediately after a crash or other accident. As a result of said tightening the person to be protected is held by the belt in his or her seat against the seat and the backrest before the person can pull out the belt owing to the inertial forces of the body of that person and his or her movement relative to the vehicle. As the belt is tightened in case of a crash or other accident, the person to be protected is virtually coupled to the seat so that he or she will participate in the deceleration of the vehicle at a very early time. The tightening of the belt will also decrease the distance over which the person to be protected can fall forwardly in case of an accident so that a strong impact of the head or other parts of the body of the person on the steering wheel or other parts of the vehicle can be prevented. On the other hand, the belt cannot be tightened by means of the belt buckle unless the belt is blocked in the belt retractor before it is tightened. That blocking is ensured in that the belt retractor is also provided with a so-called vehicle-sensitive system, which will block the belt reel in response to a lower acceleration so that the belt reel will be in a blocked state before the belt is tightened by the response of the vehicle-sensitive system for the tightener, which latter system is responsive to higher accelerations.